Watch these warning signs for a potential peak in the stock market's long-term bull rally, NDR says

Adobe Firefly, Tyler Le/BI

• Ned Davis Research says investors should watch for signs of a potential peak in the S&P 500.
• The secular bull market, which began in 2009, is in a mature stage according to NDR's Tim Hayes.
• "With the secular bull mature, we're watching out for signs that it may be at risk," he said.

With the S&P 500 in its 15th year of a secular bull market that started in 2009, Ned Davis Research says investors should watch for warning signs of a potential peak.